The initial assessment conducted with the Nitrogen Index at El Chupon that estimated an average residual soil NO3-N after harvesting of forage corn of 405 kg NO3–N ha−1 also estimated that the average nitrate leaching was 423 kg NO3–N ha−1. This assessment of average NO3–N ha−1 leaching at the El Chupon farm of 423 kg NO3–N ha−1 suggests that since 540 kg NO3–N ha−1 are being added to this system with irrigation water that has a background NO3-N concentration of 60 ppm, the El Chupon system is mining 117 kg NO3–N ha−1 from groundwater (540 kg NO3–N ha−1 [input with irrigation water]−423 kg NO3–N ha−1 [leached out from the 60 cm depth]=117 kg NO3–N ha−1 being mined from groundwater).